Headers refer to the structure disposed at the front of an agricultural harvesting vehicle that gather growing plant matter and cut it off, typically close to ground level. These machines may include such things as combines and windrowers, for example.
For most crops, it is important that the bottom edge of the header where the crop is cut travels very close to the ground, typically on the order of 1-6 inches away from the ground. To insure that the header follows the ground at this height, skids are provided on the bottom of the header to rest gently upon the ground, and permit the header to follow the ground contours up and down as the vehicle travels through the field.
Headers are typically heavy, however, and cannot rest with their weight entirely upon the ground. If they did, this is great weight would cause the header itself to dig into the ground and scoop up earth, rocks, sticks and similar foreign matter other than the crop that should be harvested.
To prevent the header from resting entirely upon the ground and digging into the ground, it is often counterbalanced, which reduces the force exerted by the header upon the ground. As an example, the header of a windrower may weigh 500-1000 pounds. The effective downforce that permits the windrower header to glide smoothly over the ground without digging into the soil is only about 70 pounds. To counterbalance the header of a windrower, an upward force of several hundred pounds should be applied to the header.
Arrangements called “header flotation systems” have been devised to apply this upward force to headers. Traditionally, they have included a complex arrangement of elongated springs, levers, bell cranks, and similar mechanical linkages. The goal in most header flotation systems is to apply a constant upforce on the header that is independent of the actual position of the header. While this ideal is rarely achieved, it is nonetheless the ideal, and therefore elongated springs that have a relatively flat response (i.e. a constant spring force applied to the header regardless of the length to which the spring is stretched) have traditionally been preferred. These long springs take a large amount of space and require considerable adjustment, however, particularly when changing from one header to another, or when adding or removing attachments or associated implements.
To solve this problem, many manufacturers have begun to use adjustable hydraulic springs comprised of hydraulic cylinders coupled to gas charged accumulators. Whenever the header is modified, it is relatively easy for the operator to change the strength of the hydraulic spring by varying the amount of hydraulic fluid inside the accumulator and hence varying the accumulator pressure.
In these simple systems, the operator adjusts the amount of preload by manipulating an operator input device to vary the precharge on the hydraulic cylinders that function as counterbalance springs. By increasing the fluid precharge in the accumulator, a higher counterbalance force can be applied and the header will rest more gently upon the ground. By reducing the fluid precharge in the accumulator, a lower counterbalance force can be applied and the header will rest more heavily upon the ground.
In practice, the operator adjusts the hydraulic fluid precharge inside the operator cab, then climbs down from the vehicle, walks to the front of the vehicle where the header is located, and then manually raises the header to determine what the net downforce is that the header applies to the ground. This process is repeated as many times as necessary until the operator is satisfied with the net downforce.
This process is slow. Furthermore, it is inconsistent. Even further, it does not permit the header flotation system to be easily adjusted during operation in the field. This latter situation is a particular problem since headers typically gather not only plant matter, but rocks, dirt, sand, sticks, branches, and other trash matter as they travel through the field. These rocks and trash become wedged between components of the header. Further, they can be gathered by the header and deposited inside the auger chamber, or they can be fed to the middle of the header (in the case of combine harvesters) and fall underneath and around the feeder that directs the crop matter to the threshing system.
Regardless of the method by which the non-crop matter is gathered, as it accumulates it weighs the header down and adds to the ground force applied to the header against the ground. With no easy system for accommodating this non-crop matter (e.g. by removing it quickly and easily from the header, or by increasing the counterbalance force) the net effect is for the header to press harder and harder against the ground, eventually requiring the operator to stop the vehicle and either increase the counterbalance force, or clean out the header.
What is needed, therefore, is a system for quickly and easily setting the counterbalance force applied to the header, and hence setting the downforce of the header acting upon the ground. What is also needed is a system for accommodating changes in header weight due to non-crop matter such as rocks and trash gathered into the header. It is an object of this invention to provide a header flotation system that provides these benefits.